linux-kernel - [ 10/41] mm: vmscan: fix force-scanning small targets without swap

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Message-Id: <20120730172902.122939996@linuxfoundation.org>
Date:	Mon, 30 Jul 2012 10:31:09 -0700
From:	Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:	linux-kernel@...r.kernel.org, stable@...r.kernel.org
Cc:	Greg KH <gregkh@...uxfoundation.org>,
	torvalds@...ux-foundation.org, akpm@...ux-foundation.org,
	alan@...rguk.ukuu.org.uk, Johannes Weiner <jweiner@...hat.com>,
	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>,
	Michal Hocko <mhocko@...e.cz>, Ying Han <yinghan@...gle.com>,
	Balbir Singh <bsingharora@...il.com>,
	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>,
	Daisuke Nishimura <nishimura@....nes.nec.co.jp>,
	Mel Gorman <mel@....ul.ie>, Mel Gorman <mgorman@...e.de>
Subject: [ 10/41] mm: vmscan: fix force-scanning small targets without swap

From: Greg KH <gregkh@...uxfoundation.org>

3.0-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Johannes Weiner <jweiner@...hat.com>

commit a4d3e9e76337059406fcf3ead288c0df22a790e9 upstream.

Stable note: Not tracked in Bugzilla. This patch augments an earlier commit
        that avoids scanning priority being artificially raised. The older
	fix was particularly important for small memcgs to avoid calling
	wait_iff_congested() unnecessarily.

Without swap, anonymous pages are not scanned.  As such, they should not
count when considering force-scanning a small target if there is no swap.

Otherwise, targets are not force-scanned even when their effective scan
number is zero and the other conditions--kswapd/memcg--apply.

This fixes 246e87a93934 ("memcg: fix get_scan_count() for small
targets").

[akpm@...ux-foundation.org: fix comment]
Signed-off-by: Johannes Weiner <jweiner@...hat.com>
Acked-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
Reviewed-by: Michal Hocko <mhocko@...e.cz>
Cc: Ying Han <yinghan@...gle.com>
Cc: Balbir Singh <bsingharora@...il.com>
Cc: KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>
Cc: Daisuke Nishimura <nishimura@....nes.nec.co.jp>
Acked-by: Mel Gorman <mel@....ul.ie>
Signed-off-by: Andrew Morton <akpm@...ux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@...ux-foundation.org>
Signed-off-by: Mel Gorman <mgorman@...e.de>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>

---
 mm/vmscan.c |   27 ++++++++++++---------------
 1 file changed, 12 insertions(+), 15 deletions(-)

--- a/mm/vmscan.c
+++ b/mm/vmscan.c
@@ -1747,23 +1747,15 @@ static void get_scan_count(struct zone *
 	u64 fraction[2], denominator;
 	enum lru_list l;
 	int noswap = 0;
-	int force_scan = 0;
+	bool force_scan = false;
 	unsigned long nr_force_scan[2];
 
-
-	anon  = zone_nr_lru_pages(zone, sc, LRU_ACTIVE_ANON) +
-		zone_nr_lru_pages(zone, sc, LRU_INACTIVE_ANON);
-	file  = zone_nr_lru_pages(zone, sc, LRU_ACTIVE_FILE) +
-		zone_nr_lru_pages(zone, sc, LRU_INACTIVE_FILE);
-
-	if (((anon + file) >> priority) < SWAP_CLUSTER_MAX) {
-		/* kswapd does zone balancing and need to scan this zone */
-		if (scanning_global_lru(sc) && current_is_kswapd())
-			force_scan = 1;
-		/* memcg may have small limit and need to avoid priority drop */
-		if (!scanning_global_lru(sc))
-			force_scan = 1;
-	}
+	/* kswapd does zone balancing and needs to scan this zone */
+	if (scanning_global_lru(sc) && current_is_kswapd())
+		force_scan = true;
+	/* memcg may have small limit and need to avoid priority drop */
+	if (!scanning_global_lru(sc))
+		force_scan = true;
 
 	/* If we have no swap space, do not bother scanning anon pages. */
 	if (!sc->may_swap || (nr_swap_pages <= 0)) {
@@ -1776,6 +1768,11 @@ static void get_scan_count(struct zone *
 		goto out;
 	}
 
+	anon  = zone_nr_lru_pages(zone, sc, LRU_ACTIVE_ANON) +
+		zone_nr_lru_pages(zone, sc, LRU_INACTIVE_ANON);
+	file  = zone_nr_lru_pages(zone, sc, LRU_ACTIVE_FILE) +
+		zone_nr_lru_pages(zone, sc, LRU_INACTIVE_FILE);
+
 	if (scanning_global_lru(sc)) {
 		free  = zone_page_state(zone, NR_FREE_PAGES);
 		/* If we have very few page cache pages,


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